What exit polls are you talking about? Are you asserting that the CNN exit poll only used Hawaii?
See how IRS was able to target the TEAParty by selecting a couple of key words to use to select applications. Think of exit polling the same way. A key word would be Hawaii. Another key word would be Chicago, another Philadelphia ~ and so on.
South Asians are even more difficult to target that way because they tend to be much more integrated than the East Asians. Still, there aren't really enough of either to make it possible to run a statistically valid exit poll to determine their preferences.